Cathode for electrolytic machining



Aue-15,1967 CHAUGER ETAL 3,336,23

cATHoDE FOR ELECTROLYTIC MACHINING Filed'June me wy 1H. m a

United States Patent O 3,336,213 CATHODE FOR ELECTROLYTIC MACHINING Claude H. Auger and James D. Andrews, Cincinnati,

Ohio, assignors to General Electric Company, a corporation of New York Filed June 19, 1963, Ser. No. 288,975 1 Claim. (Cl. 204-2Z4) This invention relates to electrolytic machining, and more particularly to an improved cathode of increased life for use in electrolytic machining.

Paralleling the development of new and difficult to machine high temperature materials has been the development of the removal of material by electrolytic means. During the operation of an electrolytic material removal process, a cathodic-tool, sometimes referred to herein as a cathode, approaches an anodic-workpiece, sometimes referred to herein as an anode, while an electrolyte is passed lbetween the cathode and the anode. When the cathode and anode are sufficiently close to one another, a deplating type of action -occurs at the anode. Such a process as this has been described in great detail in the literature and patent art as well as in co-pending application S.N. 823,975, Crawford et al., filed June 30, 1959, and now abandoned, and assigned to the assignee of the present invention.

In the generation of cavities having a relatively small `diameter compared with its length, it is -generally necessary yto apply to the outer portions of a cathode a dielectric portion such as a coating which will prevent the electrolytic action from taking place between the sides of the cathode and the .penetrated portion of the workpiece.

One of the problems with the use of such dielectric portions or coatings is that the dielectric material at the tip or end of the cathode, referred to herein as the working end portion, which iirst enters the surface of the workpiece is subject to considerable wear, abrasion and chipping action. Once part of the dielectric material at the working end portion is removed, side electrolytic action can occur, thus resulting in non-uniformity of the cavity produced and reduction in the usefulness of or damage to the cathode. Generally replacement of the cathode is required.

An object of the Ipresent invention is to provide a cathode for electrolytic machining having and improved working end portion.

Another object is to provide a cathode having a wear resistant outer peripheral portion including the working end portion.

These and other objects and advantages will lbe recognized from the following more detailed description which is meant to be exemplary of rather than a limitation on the scope of the present invention.

In the drawings:

FIG. l is a cross-sectional view of a hollow tubular form of the .present invention having an improved working end portion;

FIG. 2 is a cross-sectional view of the cathode of the present invention having an .improved outer peripheral wear resistant surface; and

FIG. 3 is an isometric partially sectional view of a solid rectangular cathode including an improved .tip portion according to the present invention.

Briefly, in one form, the cathode of the present invention has a working end portion to cooperate with an anodic workpiece as a cathode in electrolytic machining, the working end portion comprising an electrically conductive inner portion, an intermediate portion of a dielectric material and an uncharged outer metalli-c portion electrically insulated from the current carrying inner portion.

3,336,213 Patented Aug. 15, 1967 A preferred form of the present invention, particularly useful for the generation of long small diameter passages in jet engine turbine blades, comprises a hollow tubular metallic inner portion, a cured dielectric plastic intermediate coating and an outer metallic sleeve inserted in the cured plastic coating flush with the peripheral sides of the coating yet electrically insulated from the inner portion by a part of the dielectric coating.

Cooling passaegs in jet engine turbine blading have been generated through the use of electrolytic machining processes. In one instance, in `the manufacture of such blading from the nickel base super alloys, such as M-252 nickel base alloy currently available lcommercially, a number of passages for the flow of cooling air were generated through each blade from the blade tip to the blade shank portion near the blade base. Such passages were, in some instances, in the shape of a hollow tubular passage having a length of about 6 or 7 inches and a diameter of less .than 0.030 inch.

Initially, in the generation of such passages, a cathode or tool in the form of a hollow tube was tried. However, it was recognized that as the cathodic .tube penetrated farther and farther into the workpiece, an increasing amount of side electrolytic action occurred through the electrolyte between -the outer lateral surface of the tube and the workpiece. Furthermore, there is .the probability of short circuiting because of contact between the bare cathodetool and the anode workpiece. Thus a dielectric portion, for example a coating of cured epoxy resin or a plastic tetrailuoroethylene polymer coating was applied .to the outer lateral surface of the cathode. Such a dielectric portion concentrates at the working end portion the current flow through 4the electrolyte and obviates the short circuiting and side electrolytic effects -described above.

In order to generate many closely spaced air cooling passages in an article as a turbine blade, it is essential that the cathodes be very accurately dimensioned and of unusual straightness. Thus .the cost of a suitable hollow tubular cathode is relatively great compared with ordinary tubing. In the production of a large number of air cooled turbine blades, a large number of cathodes are required. However, it was recognized that the usefulness and life of the cathodic tubes was seriously limited by abrasive or chipping action occurring at the working end of the cathode on the dielectric coating. It has been found, through the use of the present invention, that .the useful life of a cathode can Abe extended in the order of about 50 times or more by the addition to the outer peripheral portion of the dielectric material of a metallic, uncharged, portionor sleeve particularly at the working end portion of the cathode.

In FIG. 1, the cathode shown generally at 10 has an uncharged metallic portion 12 embedded at the working end portion 18 in dielectric material 14. Thus .the cathode in FIG. 1, in the form of a hollow metallic t-ube, has an electrically conductive inner portion 16, an intermediate portion 14 of a dielectric material and an uncharged outer metallic portion 12 electrically insulated from the current carrying inner portion.

In one specific example, the electrically conductive inner portion is a hollow titanium tube with an intermediate dielectric coating of a plastic tetrafluoroethylene polymer sometimes referred to as Teflon material. A titanium tip or sleeve is embedded in the dielectric portion 14 and insulated `by means of that dielectric portion from the inner conductive member 16. Thus, during electrolytic action with an anodic workpiece, the cathode of FIG. 1 will allow current to flow from the working end portion 18 of inner member 16 while metallic member -12 protects the tip portion from wear and abrasion.

FIG. 2 shows another embodiment of the present invention wherein the outer lateral surface of inner member 16 is first covered with a dielectric coating around which is placed an outer metallic portion 12, included at the tip portion as well as along the sides of the cathode. Such an outer portion 12 can be slipped or pressed over the dielectric material or can be electroplated orl electroformed in place by standard, well known electrodeposition practices after first sensitizing the surface of the dielectric material. The sensitizing can be accomplished by chemically reducinga flash coating, such as of silver from a silver nitrate solution, onto the surface of the dielectric material. Then standard electrodeposition practices can be used to coat the initial flash coat of silver with other stronger, tougher metals. This practice of electroplating or electroforming the outer metallic, uncharged portion is especially useful in the preparation of solid or hollow cathodes having irregularly shaped outer dimensions.

Such an irregularly shaped cathode is the composite solid cathode shown in FIG. 3 wherein over inner conductive member 16 is an intermediate dielectric portion 14 and an electroformed uncharged outer metallic portion 12 at its working end 18. It will be recognized that inner member 16 can be hollow without departing from the scope of `the .present invention.

Although the present invention has been described in connection with specific examples, it will be readily recognized by those skilled inthe art the variations and modications of which the invention is capable.

What is claimed is:

Electrolytic machining apparatus comprising in combination an improved cathodic-tool including a Working end portion to cooperate with a workpiece in electrolytic machining, the working end portion comprising:

(a) an electrically conductive hollow inner portion at the working end portion; (b) an intermediate portion of a dielectric material encasing the entire outer lateral surface of the inner por-tion; and (c) an uncharged outer metallic portion encasing and embedded in the outer lateral surface of the intermediate portion at the working end portion and electrically insulated from the inner portion; an electrical power source; electrical conductor means connected between the cathodic-tool and the workpiece whereby the cathodic-tool is cathodic and the workpiece is anodic during electrolytic machining; means to introduce electrolyte Ibetween the cathodictool and the workpiece through the hollow electrically conductive inner portion from the open working end portion; and means to move the cathOdic-tool and the workpiece one toward the other during electrolytic machining.

References Cited UNITED STATES PATENTS 3,278,411 10/1966 Williams 204-143 FOREIGN PATENTS 1,307,441 9/ 1962 France.

938,516 10/ 1963 Great Britain.

JOHN H. MACK, Primary Examiner,

W. VAN SISE, Assistant Examiner. 

